Campylobacter research at IFR

Campylobacter research at IFR

Introduction

Campylobacter research at the Institute of Food Research (IFR) focuses on understanding the molecular processes involved in Campylobacter infections. State-of-the art techniques are used or developed for the analysis of virulence gene regulation and bacterial responses to stresses encountered during infection of avian and mammalian hosts or during survival in the environment. The aim is to provide an integrated, holistic approach to the investigation of Campylobacter biology and pathogenesis of infection, by combining both the study of Campylobacter physiology and genetics.

The overlying theme of the IFR Campylobacter research is to provide an integrated, holistic approach combining both physiology and genetics to study the biology of Campylobacter. Through our own research and through carefully selected collaborations we hope to understand the parameters underlying adaptation to different stresses relevant in the food chain, virulence, and strain variability, and then use these parameters to get a grip on the underlying physiology of these processes. Campylobacter research has long suffered from a lack of tools to manipulate the organism, and together with some special features of its infection cycle the bacterium provides a unique challenge. A better understanding of the underlying biology could support the identification of handles allowing control of this pathogen. The research has been subdivided in different approaches, which share the common overlying theme of the IFR Campylobacter research.

Research objectives

Objective 1. Stress Responses: To define the response of Campylobacter to the diverse stresses encountered during infection of the human and avian GI tract
This project focusses on the molecular mechanisms driving the response to stresses relevant to infection of the human and avian GI tract, and will include stresses relevant to other parts of the food chain. We will perform in vitro studies to identify the physiological responses of C. jejuni to the key environmental stresses that are found in food-associated, intracellular and gastrointestinal situations and are relevant to bacterial survival and virulence. Transcriptomic, proteomic and metabolomic approaches as well as more focussed molecular and biochemical approaches will be combined using the modelling expertise present at IFR, thus exploiting the wealth of possibilities and expertise present at IFR. Campylobacter can survive in a wide range of environments, as it colonises the avian gut and cecum, survives in the environment and on meat despite different hygienic precautions and during storage, and can transiently colonise the human or animal gut. The high level of colonisation of chickens suggests optimal adaptation to this environment, but its long term survival on meat and in the environment suggests the presence of alternative mechanisms for stress survival. One of the possible survival mechanisms of C. jejuni in the environment and on meat may be through formation or participation in biofilms. Alternatively, the cell can adapt its cellular machinery to a sort of dormant state associated with long term survival. Opposite to adaptation for long term survival is the adaptation to rapid changes in conditions as are thought to occur during colonisation of mammalian and avian organs. The innate and adaptive host immune system will form barriers that Campylobacter wil have to overcome, and there are also chemical stresses like pH during gastric passage, and the competition with the resident gut flora. These stresses require rapid adaptation, often mediated through changes in gene expression via transcriptional or post-transcriptional regulation.

 

Objective 2. Genetic Responses: To define the mechanisms driving genomic variation and virulence in Campylobacter
Human infection with Campylobacter can manifest symptoms that range from mild watery to severe bloody diarrhoea. This variation is likely to be affected by several factors including host genetics and immune status, infective dose and bacterial genetics. Strain variation exists in Campylobacter as an adaptive mechanism to avoid host defences and bacteriophage susceptibility and occurs at the level of interstrain variability where up to 20% of the genomic content can be different between strains, as well as phenotypic variation within strains via hypervariable sequences in genes, e.g. phase variation via homopolymeric mono- and dinucleotide tracts. The resulting variation can have a significant effect on the population structure, which potentially could lead to quasi-species development as has been suggested for H. pylori.

 

Objective 3. Metabolic responses: to define the metabolic pathways used by Campylobacter in its growth cycle
Although the complete genome sequence of C. jejuni has been available since 2000, many questions about metabolism of C. jejuni are still open. Much of the attention in the earlier years has been on mechanisms of virulence, thus delaying any detailed investigations on C. jejuni metabolism. We intend to use data mining combined with the metabolomic facilities at IFR to study different novel metabolic pathways suggested to be present in C. jejuni, which could subsequently lead to the formulation of novel antimicrobial agents or intervention strategies.

 

Objective 4. Host responses: to define immune responses involved in Campylobacter-induced disease
This novel objective will focus on the differences between mammalian and avian hosts in outcome of infection with C. jejuni; mammalian hosts exhibit diarrhoeal symptoms, but avian hosts do not, and appear to tolerate C. jejuni as a commensal species. The hypothesis is that differences in the expression of pathogenic factors and a milder immune response in chickens may be responsible for this phenomenon.

 

Objective 5. Development and extension of the Campylobacter genetic toolbox
C. jejuni is difficult to manipulate genetically, especially when compared to well know bacterial pathogens like Salmonella and E. coli. Despite our efforts, there is still a lack of systems for convenient complementation, conditional mutations, null-mutations and reporter gene expression. We aim to develop and improve such techniques when required. The genetic tools available for use with Campylobacter are limited in comparison with other prokaryotes, and this limits the nature of work that can be performed. In order to alleviate this restriction we have started to develop methods for the simple construction of gene complementation and gene reporter strategies. The gene complementation methods will allow the use of both native and non-native promoters to control the expression of the target gene(s). Initially, the reporter system will utilise GFP fusions with the promoter(s) of interest, although other reporter assays are being considered.